Solar energy water heating system

ABSTRACT

In one aspect, the invention is directed to a solar energy water heating system for heating water in a water storage tank. In one particular embodiment, the system includes a controller, a solar energy collector whose energy contribution to water in the tank is controlled by the controller, and a non-solar heating system that is not controlled by the controller. Water in the tank may be heated by one or both of the non-solar heating system and energy from the solar energy collector. The controller can determine the amount of energy contributed by solar energy to the water in the tank. In another embodiment, the solar energy water heating system incorporates a controller that controls both the operation of the pump and the operation of the non-solar heating system. In another embodiment, a network of solar energy water heating systems is provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. patent application61/100,002, filed Sep. 25, 2008, which is incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to a solar energy water heating system,network and method, particularly to a solar energy water heating systemthat heats water using a combination of solar energy and a non-solarheating system, and more particularly to a solar energy water heatingsystem that heats water using a combination of solar energy and anelectric heating system.

BACKGROUND OF THE INVENTION

In homes, other residential buildings, commercial buildings andindustrial buildings, a hot water tank is typically provided so that hotwater is readily available for use by a user for a variety of purposes.A heating system that may be powered by electricity, natural gas, oil,propane or by some other means is provided for heating water in thetank. The heating system, however, can be expensive to operate due tothe cost of electricity or fuel. Some systems have been proposed thatincorporate solar energy collectors for the purposes of heating water inthe hot water tank. Such systems, however, may include a non-solarheating system, such as an electric heating system, but may lack controlover the non-solar heating system, and may also lack the ability todetermine the savings achieved by the use of the solar energy collector.

It would be advantageous to provide a solar energy water heating systemthat overcomes one or more of the problems described above.

SUMMARY OF THE INVENTION

In one aspect, the invention is directed to a solar energy water heatingsystem for heating water in a water storage tank. In one particularembodiment, the system includes a controller, a solar energy collectorwhose energy contribution to water in the tank is controlled by thecontroller, and a non-solar heating system that is not controlled by thecontroller. Water in the tank may be heated by one or both of thenon-solar heating system and energy from the solar energy collector. Thecontroller can determine the amount of energy contributed by solarenergy to the water in the tank. In another embodiment, the solar energywater heating system incorporates a controller that controls both theoperation of the pump and the operation of the non-solar heating system.In another embodiment, a network of solar energy water heating systemsis provided.

In a first embodiment, the invention is directed to a solar energy waterheating system comprising a water storage tank, a non-solar heatingsystem configured to heat water in the water storage tank, a thermostatpositioned to sense the temperature indicative of the temperature ofwater in the water storage tank, a solar energy collector, a heatexchanger, a first fluid circuit between the solar energy collector andthe heat exchanger, a pump configured to pump fluid through the firstfluid circuit, a second fluid circuit between the water storage tank andthe heat exchanger, and a controller. The second fluid circuit isfluidically connectable to a water source. The heat exchanger isconfigured to transfer heat from fluid in the first fluid circuit towater in the second fluid circuit. The thermostat is operativelyconnected to the non-solar heating system. The controller is configuredto control the operation of the pump. The controller is furtherconfigured to receive non-solar heating system state signals indicativeof whether the non-solar heating system is on and is configured todetermine the amount of energy transferred from the solar energycollector to water in the water storage tank based at least in part onthe non-solar heating system state signals.

In a second embodiment, the invention is directed to a solar energywater heating system comprising a water storage tank, a non-solarheating system configured to heat water in the water storage tank, asolar energy collector, a heat exchanger, a first fluid circuit betweenthe solar energy collector and the heat exchanger, a pump configured topump fluid through the first fluid circuit, a second fluid circuitbetween the water storage tank and the heat exchanger, a storage tankwater temperature sensor, and a controller. The second fluid circuit isfluidically connectable to a water source. The heat exchanger isconfigured to transfer heat from fluid in the first fluid circuit towater in the second fluid circuit. The controller is configured toreceive signals from the storage tank water temperature sensorindicative of the temperature of water in the water storage tank. Thecontroller is configured to prevent operation of the pump if the signalsfrom the storage tank water temperature sensor indicate the temperatureof water in the water storage tank exceeds a predetermined high storagetank water temperature.

In a third embodiment, the invention is directed to a solar energy waterheating system comprising a water storage tank, a solar energycollector, a heat exchanger, a first fluid circuit between the solarenergy collector and the heat exchanger, a pump configured to pump fluidthrough the first fluid circuit, a second fluid circuit between thewater storage tank and the heat exchanger, a solar energy collectortemperature sensor positioned to sense temperature indicative of thetemperature of the solar energy collector, a source water temperaturesensor positioned to sense temperature indicative of the temperature ofwater from the water source and a controller. The second fluid circuitis fluidically connectable to a water source. The heat exchanger isconfigured to transfer heat from fluid in the first fluid circuit towater in the second fluid circuit. The controller is configured toreceive solar energy collector temperature sensor signals from the solarenergy collector temperature sensor and source water temperature sensorsignals from the source water temperature sensor. The controller isfurther configured to prevent operation of the pump if either the solarenergy collector temperature sensor signals indicate a solar energycollector temperature that is below a predetermined low solar energycollector temperature or if the source water temperature sensor signalsindicate a source water temperature that is below a predetermined lowsource water temperature.

In a fourth embodiment, the invention is directed to a solar energywater heating system comprising a water storage tank, a non-solarheating system configured to heat water from the water storage tank, asolar energy collector, a heat exchanger, a first fluid circuit betweenthe solar energy collector and the heat exchanger, a pump configured topump fluid through the first fluid circuit, a second fluid circuitbetween the water storage tank and the heat exchanger, and a controllerconfigured to control the operation of the pump and the non-solarheating system. The heat exchanger is configured to transfer heat fromfluid in the first fluid circuit to water in the second fluid circuit.The second fluid circuit is fluidically connectable to a water source.

In a fifth embodiment, the invention is directed to a solar energy waterheating system for operation with a first water storage tank and anon-solar heating system configured to heat water from the first waterstorage tank. The system comprises a second water storage tank having asecond water storage tank consumption outlet that is fluidicallyconnectable to an inlet on the first water storage tank, a solar energycollector, a heat exchanger, a first fluid circuit between the solarenergy collector and the heat exchanger, a pump configured to pump fluidthrough the first fluid circuit, a second fluid circuit between thesecond water storage tank and the heat exchanger, and a controllerconfigured to control the operation of the pump and the non-solarheating system. The heat exchanger is configured to transfer heat fromfluid in the first fluid circuit to water in the second fluid circuit.The second fluid circuit is fluidically connectable to a water source.

In a sixth embodiment, the invention is directed to a method of heatingwater in a water storage tank, comprising:

a) selecting at least one heating means from a group of heating meansincluding a non-solar heating system and a solar energy collector; andb) heating water in the water storage tank using the selected heatingmeans based at least in part on the temperature of water in the waterstorage tank.

In a seventh embodiment, the invention is directed to a network of solarenergy water heating systems, comprising a central control system, and aplurality of solar energy water heating systems. Each system includes awater storage tank, a non-solar heating system configured to heat waterfrom the water storage tank, a solar energy collector, a heat exchanger,a first fluid circuit between the solar energy collector and the heatexchanger, a pump configured to pump fluid through the first fluidcircuit, a second fluid circuit between the water storage tank and theheat exchanger, and a local controller configured to control theoperation of the pump and the non-solar heating system. The heatexchanger is configured to transfer heat from fluid in the first fluidcircuit to water in the second fluid circuit. The second fluid circuitis fluidically connectable to a water source. The central control systemis configured to control the operation of the local controllers.

In an eighth embodiment, the invention is directed to a method ofheating water from a plurality of water storage tanks, comprising:

a) providing a local controller in association with each water storagetank wherein the local controller is operatively connected to anon-solar heating system for the associated water storage tank and asolar energy collector system for the associated water storage tank;b) providing a central control system that is in communication with thelocal controllers;c) selecting for each water storage tank at least one heating means froma group of heating means including a non-solar heating system and asolar energy collector;d) heating water in each water storage tank using the selected heatingmeans; ande) sending signals from one of the group consisting of the centralcontrol system and at least one local controller to the other of thegroup consisting of the central control system and at least one localcontroller, wherein the signals relate to the operation of the at leastone local controller.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described by way of example only withreference to the attached drawings, in which:

FIG. 1 is a schematic illustration of a single-tank solar energy waterheating system in accordance with an embodiment of the presentinvention;

FIG. 2 is a schematic illustration of a controller used with the solarenergy water heating system shown in FIG. 1;

FIG. 3 is a schematic illustration of another single-tank solar energywater heating system in accordance with another embodiment of thepresent invention

FIG. 4 is a schematic illustration of a controller used with the solarenergy water heating system shown in FIG. 3;

FIG. 5 is a schematic illustration of a dual-tank solar energy waterheating system in accordance with another embodiment of the presentinvention;

FIG. 6 is a flow diagram illustrating a method of heating water in awater storage tank;

FIG. 7 is a schematic illustration of a network of solar energy waterheating systems in accordance with another embodiment of the presentinvention; and

FIG. 8 is a flow diagram illustrating a method of heating water in aplurality of water storage tanks.

DETAILED DESCRIPTION OF THE INVENTION

Reference is made to FIG. 1, which shows a solar energy water heatingsystem 10 in accordance with an embodiment of the present invention. Thesolar energy water heating system 10 is used to heat water in a waterstorage tank 11 using a combination of solar energy and using anon-solar heating system 12. Using the solar energy water heating system10 to heat the water in the water storage tank 11 can reduce the energycosts associated with heating the water relative to some prior artsystems that utilizes a non-solar heating system only.

The solar energy water heating system 10 may reside in a home, amulti-unit residential building, a commercial building, an industrialbuilding or any other structure where hot water is used.

The solar energy water heating system 10 includes the water storage tank11, the non-solar heating system 12, a solar energy collector 14, a heatexchanger 16, a first fluid circuit 18 between the solar energycollector 14 and the heat exchanger 16, a pump 20 configured to pumpfluid through the first fluid circuit 18, a second fluid circuit 22between the water storage tank 11 and the heat exchanger 16, and acontroller 24.

The water storage tank 11 includes a first storage tank port 26, whichmay be a consumption outlet through which hot water is drawn for use bya user. The water storage tank 11 includes a second storage tank port 30and a third storage tank port 30, which connect the water storage tank11 to the second fluid circuit 22. The second storage tank port 30 maybe positioned approximately ⅔ of the way up the water storage tank 11.The third storage tank port 30 may be positioned proximate the bottom ofthe water storage tank 11.

The non-solar heating system 12 may be any suitable type of heatingsystem, such as, for example, an electric heating system. Alternatively,the non-solar heating system 12 may operate using oil, natural gas,propane or some other means. The non-solar heating system 12 may includea single heating element 32 which may be positioned approximately ⅔ ofthe way up the water storage tank 11, preferably slightly above theheight of the second storage tank port 30. The positioning of theheating element 32 is discussed further below.

In the embodiment shown in FIG. 1, a thermostat 33 is operativelyconnected to the non-solar heating element 12 and controls the operationof the heating element 12 based on the temperature of water in the waterstorage tank 11.

The solar energy collector 14 may be any suitable type of solar energycollector. The solar energy collector 14 may be positioned on the roofof the structure, or in some other suitable position, such as on a wallthat is oriented for exposure to the sun.

The heat exchanger 16 may be any suitable type of heat exchanger, suchas a brazed plate heat exchanger. The heat exchanger 16 includes aprimary side 34, having a primary side inlet 36 and a primary sideoutlet 38, and a secondary side 39 having a secondary side inlet 40 anda secondary side outlet 42.

A heat transfer fluid is pumped by the pump 20 through the first fluidcircuit 18. More particularly, the heat transfer fluid is pumped by thepump 20 from an expansion tank 44 to the solar energy collector 14 forheating thereby, after which the heat transfer fluid flows through theprimary side 34 of the heat exchanger 16 and back to the expansion tank44. The heat transfer fluid may be any suitable type of fluid, such as asolution of propylene glycol and water to resist freezing duringexposure to cold weather. The solution may comprise about 50 wt %propylene glycol and about 50 wt % water, or may have some other ratioor composition altogether.

Water may flow by any suitable means through the second fluid circuit22, such as by means of a temperature differential that may be presentacross the second side 39 of the heat exchanger 16. As a result of thepositioning of the heating element 32, the second storage tank port 30,and the third storage tank port 30, a temperature gradient can beintroduced in the water in the water storage tank 11 where the coldestwater is at the bottom of the tank 11, and hotter water is in the topportion of the tank 11.

Thus, circulation of water through the second fluid circuit 22 may beinduced passively (ie. without inducing water flow using a pump). Thewater may flow from the water storage tank 11 through the third storagetank port 30 into the second fluid circuit 22, upwards through thesecondary side 39 of the heat exchanger 16 and then upwards to thesecond storage tank port 30 where the water reenters the water storagetank 11. The heating element 32 may heat water in the top portion of thetank 11 to be hotter than the water entering the water storage tank 11through the second storage tank port 30.

A source water conduit 46 may be connected to a source water inlet 48into the second fluid circuit 22, which may be positioned between theheat exchanger 16 and the second storage tank port 30. The source waterconduit 46 may be connected to any suitable water source (not shown)such as a city water connection or a well. A source water flow controlvalve 50 may be provided on the source water conduit 46 to control theintroduction of source water into the second fluid circuit 22 as neededbased on the consumption of water from the water storage tank 11 throughthe consumption outlet 26. The operation of the source water flowcontrol valve 50 may be controlled by any suitable means, such as by astorage tank water level sensor (not shown). Alternatively it ispossible for the controller 24 to control the operation of the sourcewater flow control valve 50.

The heat exchanger 16 is configured to transfer heat from the heattransfer fluid in the first fluid circuit 18 to water in the secondfluid circuit 22.

The controller 24 controls the operation of the solar energy waterheating system 10. Referring to FIG. 2, the controller 24 may include aprocessor 51, a memory 52, one or more inputs 53 for receiving signalsfrom one or more sensors, and one or more outputs 54 through with thecontroller 24 sends output signals (eg. to control a system component).The one or more sensors that may be connected to the inputs 53 mayinclude, for example, a storage tank water exit temperature sensor 55(FIG. 2), a source water temperature sensor 56, a heat exchangersecondary inlet water temperature sensor 58, a solar energy collectortemperature sensor 60, a source water flow meter 62, and a non-solarheating element state sensor 64. The temperature sensors 55, 56, 58 and60 may be any suitable types of temperature sensor, such as, forexample, thermistors.

The storage tank water exit temperature sensor 55 is positioned at asuitable position to sense temperature and to send to the controller 24storage tank water temperature sensor signals that are indicative of thetemperature of hot water leaving the water storage tank 11. The storagetank water temperature sensor signals may be sent to the controller 24any suitable way, such as along an electrical conduit 66 or, forexample, via a wireless connection.

The storage tank water exit temperature sensor 55 is positioned at asuitable position to sense temperature and to send to the controller 24storage tank water temperature sensor signals that are indicative of thetemperature of the hottest water in the water storage tank 11 andindicative of the temperature of the water leaving the water storagetank 11. Thus the storage tank water temperature sensor signals from thestorage tank water exit temperature sensor 55 may be referred to as hotstorage tank water temperature sensor signals, or storage tank exitwater temperature sensor signals. These signals may be sent to thecontroller 24 any suitable way, such as along an electrical conduit 66or, for example, via a wireless connection.

The source water temperature sensor 56 and source water flow meter 62are positioned at a suitable position to sense temperature and flowrespectively and to send to the controller 24 source water temperaturesensor signals and source water flow rate signals respectively that areindicative of the temperature and flow rate of any source water enteringthe second fluid circuit 22. The source water temperature sensor signalsand source water flow rate signals may be communicated to the controller24 by any suitable means, such as along electrical conduits 68 and 70or, for example, wirelessly.

The non-solar heating element state sensor 64 is positioned at asuitable position to sense whether the non-solar heating element 12 ison or off and is configured to send to the controller 24 non-solarheating element state sensor signals that are indicative of the of thestate of the non-solar heating element 10. The structure of thenon-solar heating element state sensor 64 may depend on the structure ofthe heating element 32. For example, if the heating element 32 iselectric, then the non-solar heating element state sensor 64 may beconfigured to determine if there is current flow in the electricalconduit connecting the heating element 32 to an electrical power source.

The controller 24 may be configured to operate in one or more ways. Forexample, the controller 24 may be configured to determine the amount ofenergy transferred over a given time period from the solar energycollector 14 to water in the water storage tank 11. This may bedetermined by any suitable method. For example, it may be determinedusing energy input including: the temperature history of water in thewater storage tank 11 over the time period, the volume of water in thewater storage tank 11, the flow history and temperature history of anywater introduced to the second fluid circuit 22 from the water source,the amount of time the non-solar heating system was on over the giventime period, and the power (eg. the wattage) of the non-solar heatingsystem 12.

The difference between the current temperature of the water in the waterstorage tank 11 and the temperature at the beginning of the time periodcan be used to determine the total energy change in the water in thetank 11. These two temperatures can be obtained by any suitable means,eg. using the storage tank water exit temperature sensor 55.

The flow history and temperature history of the water introduced intothe second fluid circuit 22 from the water source (not shown) combinedwith the temperature history of the water in the water storage tank 11may be used to determine the amount of energy lost from the water in thewater storage tank 11 as a result of water consumption from the tank 11and replenishment from the water source (not shown).

The amount of time the non-solar heating system 12 was on over the giventime period and the power (eg. the wattage) of the non-solar heatingsystem 12 can be used to determine the amount of energy introduced by itinto the water in the water storage tank 11.

The total energy change of the water in the water storage tank 11, theamount of energy lost as a result of water consumption and replenishmentfrom the water source, and the amount of energy introduced by thenon-solar heating system 12 into the water in the tank 11 can be used todetermine the amount of energy introduced into the water from the tank11 by the solar energy collector 14, which may be referred to as Esolar.It will be understood that the above is but an exemplary way ofdetermining the value of Esolar using the aforementioned sensor data. Itis possible for the controller 24 to determine the value of Esolar usingthe aforementioned energy input information without specificallycalculating the individual energy contributions made by the source waterand non-solar heating element but instead to perform a single largecalculation. It is alternatively possible, for example, for thecontroller 24 to determine the value of Esolar without calculation atall, but instead to use the values from the sensors as input values fora lookup table, or by some other method that is different than usinglookup tables or calculations. As yet another alternative, thecontroller 24 may use a combination of methods, such as using bothlookup tables and calculations, to determine the value of Esolar.

As an example of a different but related approach to determining thevalue of Esolar, the controller 24 may compare the expected storage tankwater exit temperature with the actual storage tank water exittemperature. The difference between the aforementioned expected andactual temperatures may be attributed to the energy input from the solarenergy collector 14.

It is possible for the controller 24 to obtain the aforementioned energyinput information using sensor data that is stored in the memory 52. Itis alternatively possible for the controller 24 to obtain at least someof the energy input information without use of sensors. For example, thepower of the non-solar heating system 11 may be obtained without usingany sensors. It may, for example, simply be a value that is stored inthe memory 52 based on the model and type of water storage tank 11. Asanother example, the source water temperature sensor 56 may be omittedand the controller 24 may instead use an estimate of the temperature ofthe source water in its determination of Esolar. As yet another example,the source water flow meter 62 may be omitted and the controller 24 mayinstead use an estimate for the flow rate of the source water into thesecond fluid circuit 22.

Information relating to the energy input from the solar energy collector14 may be displayed on a display 74 that may be provided as part of thecontroller 24. The information displayed on the display 74 may include,for example, the energy saved, the amount of carbon saved, and/or themoney saved by using the solar energy water heating system 22. Thedisplay 74 may be positioned with the other components of the controller24 or may be remotely positioned for convenient viewing by a user of thesolar energy water heating system 22. For example, the display 74 may bein a main floor hallway of a house, and may communicate wirelessly (orby electrical conduit) with the rest of the controller 24 which may bepositioned proximate the pump 20 and water storage tank 11 in a furnaceroom on a basement level of the house.

The controller 24 may include an output 54 through which it controls theoperation of the pump 20 based on signals from one or more of thesensors. For example, the controller 24 may be configured to start thepump 20 if the temperature of the water leaving the water storage tank11 is less than a predetermined low storage tank water exit temperature.Starting the pump 20 initiates flow in the first fluid circuit 18, whichgenerates heat transfer from the solar energy collector 14 into the heattransfer fluid, which in turn generates heat transfer from the firstfluid circuit 18 to the water in the second fluid circuit 22 through theheat exchanger 16. In embodiments wherein the thermostat 33 isoperational and is operatively connected to the non-solar heatingelement 32, the predetermined low storage tank water exit temperature ishigher than the temperature at which the thermostat 33 activates thenon-solar heating element 32.

The controller 24 may check for one or more of a plurality of conditionswhen determining whether or not to turn on or turn off the pump 20. Forexample, if the controller 24 receives signals from the solar energycollector temperature sensor 60 and the heat exchanger secondary inletwater temperature sensor 58 and determines that the temperaturedifference therebetween is less than a predetermined thresholdtemperature difference, the controller 24 may prevent operation of thepump 20. Because the operation of the pump 20 itself consumes energy,the amount of energy saved by heating the storage tank water using thesolar energy collector 14 only offsets the energy consumed by the pump20 if the temperature difference is sufficiently large between the heattransfer fluid and the water. The predetermined threshold temperaturedifference may be any suitable amount, such as, for example, about 10degrees Celsius.

As another example, if the controller 24 receives signals from thestorage tank water exit temperature sensor 55 indicating that the waterleaving the water storage tank 11 exceeds a predetermined high storagetank water exit temperature, the controller 24 is configured to preventoperation of the pump 20 to inhibit any further heating of the water bythe solar energy collector. The predetermined high storage tank waterexit temperature may be about 85 degrees Celsius.

As another example, if the controller 24 receives signals from the solarenergy collector temperature sensor 60 indicating that the solar energycollector 14 is less than a predetermined low solar energy collectortemperature, or if the controller 24 receives signals from the sourcewater temperature sensor 56 indicating that the source water is lessthan a predetermined low source water temperature, then the controller24 may prevent operation of the pump 20 to inhibit exposure of the solarenergy collector 14 an the heat exchanger 16 respectively to freezingconditions. The predetermined low solar energy collector temperature maybe any suitable temperature, such as, for example, about 4 degreesCelsius. Below this temperature, there is a risk of the heat transferfluid thickening in consistency (becoming gel-like) and becomingdifficult to pump using the pump 20. In a thickened state, the heattransfer fluid could possibly cause damage to the pump 20 if an attemptwere made by the pump 20 to pump it.

The predetermined low source water temperature may be any suitabletemperature, such as, for example, about 4 degrees Celsius.

Optionally, a suitable flow cut-off valve 78 may be provided between thesource water inlet 48 and the second storage tank port 30. Periodically,the flow cut-off valve 78 may be closed and the source water flowcontrol valve 50 may be opened to direct source water to flow throughthe heat exchanger 16 an into the water storage tank 11 through thethird port 20, to flush the heat exchanger 16 of deposits of mineralsand the like, such as calcium carbonate, that can build up therein. Theflow cut-off valve 78 may be closed whenever the source water flowcontrol valve 50 is opened, and the operation of the flow cut-off valve78 may be related to the operation of the source water flow controlvalve 50, such that when the valve 50 opens, the valve 78 closes andwhen the valve 50 closes the valve 78 opens. The flow cut-off valve 78may be controlled by any suitable means. For example, the cut-off valve78 may be electrically connected to the source water flow control valve50 so that when the valve 50 is open, the electrical connection isconfigured to close the valve 78 and when the valve 50 is closed, theelectrical connection is configured to open the valve 78. The structure,control and operation of the flow cut-off valve 78 may be as describedin U.S. Pat. No. 6,827,091 (Harrison). It is optionally possible for thecontroller 24 to include an output 54 (FIG. 2) through which it controlsthe operation of the flow cut-off valve 78.

Reference is made to FIG. 3, which shows a solar energy water heatingsystem 100 in accordance with another embodiment of the presentinvention. The solar energy water heating system 100 may be similar tothe solar energy water heating system 10 (FIG. 1) except that the solarenergy water heating system 100 includes a controller 102 instead of thecontroller 24 (FIG. 1), which controls the operation of both the pump 20and the non-solar heating system shown at 104. The non-solar heatingsystem 104 includes a non-solar heating element 106 that may be similarto the non-solar heating element 32 (FIG. 1).

There are many features that can be provided to the solar energy waterheating system 100 as a result of controlling both the pump 20 and thenon-solar heating system 104 with the controller 102, in addition tohaving the features described with respect to the controller 24 of FIG.2. For example, the controller 102 may be configured to control thefirst non-solar heating system 104 and the pump 20 based on signals fromthe storage tank water exit temperature sensor 55. As an example of howthis control of both heating means (ie. of both the pump 20 and thenon-solar heating system 104) could be carried out, if the storage tankwater exit temperature sensor 55 senses a temperature that is lower thana first predetermined low storage tank water exit temperature, then thecontroller 102 may start the pump 20. If the storage tank water exittemperature sensor 55 senses a temperature that is lower than a secondpredetermined low storage tank water exit temperature that is lower thanthe first predetermined low storage tank water exit temperature, thenthe controller 102 may turn on the non-solar heating system 104.

The controller 102 may select which of the heating means (ie. which ofthe pump 20 and the non-solar heating system 104) to use to heat waterin the water storage tank 11 based on one or more conditions. One suchcondition is the amount of time to heat the water in the water storagetank 11. For example, the controller 102 may be configured to determinethe expected length of time required to heat up water in the waterstorage tank 11 from a current temperature to a target temperature usingonly energy from the solar energy collector 14. If the expected lengthof time is not more than a predetermined maximum acceptable length oftime, then the controller 102 may start the pump 20 and heat the waterin the water storage tank 11 using only energy from the solar energycollector 14. If, however, the expected length of time exceeds thepredetermined maximum acceptable length of time, then the controller 102may heat the water using the non-solar heating system 104 and optionallyalso using energy from the solar energy collector 14.

The controller 102 may be configured to control the operation of thepump 20 and the first non-solar heating system 104 differently atdifferent times of the day. For example, during daytime hours theelectrical demands on a utility company may be higher than the demandsat night. The hours during which demand is higher may be referred to aspeak hours. During these peak hours, energy may be more expensive andthere is therefore incentive to reduce energy consumption during peakhours. During these peak hours, the maximum acceptable length of timemay be increased to increase the range of situations in which thecontroller 102 will opt to heat the water in the water storage tank 11solely with energy from the solar energy collector 14. During off-peakhours, the maximum acceptable length of time may be reduced toaccelerate the heating of the water in the water storage tank 11 withoutincurring excessive energy costs. Even in jurisdictions wherein a localutility company does not charge higher rates for energy during peakhours, the controller 102 may still increase the maximum acceptablelength of time during at least some daytime hours, since in a typicalhome the rate of consumption of hot water may be low relative to therate of consumption during the early morning and during the evening.

The controller 102 may be configured to operate on a rate basis. Forexample, the controller 102 may compare the rate at which hot water isbeing drawn from the water storage tank 11 with the rate at which waterin the water storage tank 11 can be heated to a target temperaturesolely using energy from the solar energy collector 14. If the result ofthe comparison indicates that the water in the water storage tank 11would increase in temperature at an acceptable rate over time, then thecontroller 102 may heat the water in the water storage tank 11 solelyusing energy from the solar energy collector 14. Conversely, if theresult of the comparison indicates that the temperature of water in thefirst water storage tank 112 would decrease over time or would notincrease sufficiently quickly, then the controller 102 may activate thenon-solar heating system 104, and may optionally also activate the pump20.

The controller 102 may be configured to heat the water in the firstwater storage tank 112 using a control algorithm. For example, thecontroller 102 may be configured to heat the water using a PID-based(ie. a proportional integral-derivative-based) control algorithm, aPI-based (ie. a proportional integral-based) control algorithm, aP-based (ie. a proportional-based) control algorithm, fuzzy logic or anyother suitable algorithm.

Reference is made to FIG. 4, which shows a schematic illustration of thecontroller 102. The controller 102 may be similar to the controller 24(FIG. 2), except that the input 53 (FIG. 2) that is connected to anon-solar heating system state sensor 64 is replaced by an output 54that is connected to the non-solar heating system 104.

Reference is made to FIG. 5, which shows a solar energy water heatingsystem 110 in accordance with another embodiment of the presentinvention. The solar energy water heating system 110 may be similar tothe solar energy water heating system 10 except that the solar energywater heating system 110 includes a water storage tank 112 with nonon-solar heating system associated therewith, upstream from apre-existing, second water storage tank 114.

The solar energy water heating system 110 includes the water storagetank 112, which may be referred to as a first water storage tank 112,the solar energy collector 14, the heat exchanger 16, the first fluidcircuit 18 between the solar energy collector 14 and the heat exchanger16, the pump 20, a second fluid circuit 116 between the first waterstorage tank 112 and the heat exchanger 16, and a controller 117.

The pre-existing, second water storage tank 114 may be a typical waterstorage tank and may have a consumption outlet 118, a second storagetank port 120 and a third storage tank port 122. Water in thepre-existing water storage tank 114 may be heated by a non-solar heatingsystem 124, which may include a first non-solar heating element 126 anda second non-solar heating element 128. The first and second non-solarheating elements 126 and 128 may be controlled by a thermostat 130.

The first water storage tank 112 includes a consumption port 132, asecond storage tank port 134 and a third storage tank port 136. Aconsumption fluid conduit 138 may connect the consumption port 132 toeither the second storage tank port 120 or the third storage tank port122 on the pre-existing, second water storage tank 114. The temperaturesensor 55 may be positioned on the consumption fluid conduit 138,preferably proximate the consumption port 118.

The second fluid circuit 116 may be similar to the second fluid circuit22 in FIG. 1. The second storage tank port 134 may be positioned on thetop of the first water storage tank 112 instead of being about ⅔ of theway up. The third storage tank port 136 may be positioned proximate thebottom of the tank 112. As a result of the positions of the second andthird storage ports 134 and 136, a temperature gradient is set upthroughout the entire height of the tank 112 to drive the flow of waterthrough the second fluid circuit 116.

The controller 117 may be similar to the controller 24 (FIG. 1). Thesolar energy water heating system 110 may lack a non-solar heatingsystem sensor however. Thus, it is possible that the controller 117 maynot receive information regarding the state of the non-solar heatingsystem 124. The controller 117 may nonetheless be capable of determiningthe energy contributed to the water stored in the first water storagetank 112 since there is no non-solar heating system associated with thattank.

The controller 117 may include several of the features associated withthe controller 24 (FIG. 1). For example, the controller 117 may beconfigured to prevent operation of the pump 20 if the temperaturessensed by the solar energy collector temperature sensor 60 and by thesource water temperature sensor 56 are less than a predetermined lowsolar energy collector temperature and a predetermined low source watertemperature respectively, both of which may be any suitable value, suchas about 4 degrees Celsius.

It is optionally possible to provide a system similar to the system 110wherein the thermostat 130 is disabled and the pre-existing non-solarheating system 124 is controlled by the controller 117.

Reference is made to FIG. 6, which illustrates a method 200 of heatingwater in a water storage tank in accordance with another embodiment ofthe present invention, which can be carried out using the system 100shown in FIG. 3, or which may alternatively be carried out by any othersuitable system.

The method 200 includes a step 202 wherein at least one heating means isselected from a group of heating means including a non-solar heatingsystem and a solar energy collector, and a step 204 which includesheating water in the water storage tank using the selected heating meansbased at least in part on the temperature of water in the water storagetank.

At step 206, the expected length of time for water in the water storagetank to be heated using only energy from the solar energy collector to atarget temperature is determined. If the expected length of time exceedsa predetermined maximum acceptable length of time then the water fromthe water storage tank may be heated using the non-solar heatingelement.

As noted with respect to the exemplary system 100 shown in FIG. 3, theat least one heating means selected in step 204 may be selected based onthe time of day. For example, if the time of day falls within a firstportion of the day, then at least the non-solar heating element isselected if the expected length of time determined in step 206 exceedsthe predetermined maximum acceptable length of time. If the time of dayfalls within a second portion of the day, which may, for example,correspond to peak hours of energy demand, then at least the solarenergy collector is selected regardless of the expected length of timeassuming that other conditions do not preclude the operation of thepump, such as the temperature of the solar energy collector.

Prior to step 202, the method 200 may include a step 208 of determiningthe rate of consumption of hot water from the water storage tank anddetermining whether the solar energy collector is capable of heating thewater in the water storage tank sufficiently quickly to compensate forthe flow of source water into the water storage tank. The method 200 mayfurther entail heating water in the water storage tank according to acontrol algorithm. The control algorithm may be any suitable type ofcontrol algorithm, such as a PID control algorithm.

Reference is made to FIG. 7, which shows a network of solar energy waterheating systems 300 in accordance with another embodiment of the presentinvention. The network of solar energy water heating systems 300includes a central control system 302, and a plurality of solar energywater heating systems 304. Each solar energy water heating system 304may be similar to the solar energy water heating system 100 (FIG. 3),and includes the solar energy collector 14, the heat exchanger 16, thefirst fluid circuit 18 between the solar energy collector 14 and theheat exchanger 16, the pump 20, a second fluid circuit 22 between theheat exchanger 16 and the first water storage tank 11. Each solar energywater heating system 304 further includes a local controller 308 whichis configured to control at least the operation of the pump 20 and thenon-solar heating system 104 and which is configured to be controlled bythe central control system 302. The communication between the centralcontrol system 302 and the local controllers 308 may be one-waycommunication from the local controllers 308 to the central controlsystem 302, one-way communication from the central control system 302 tothe local controllers 308, or may be two-way communication between thelocal controllers 308 and the central control system 302. For example,the central control system 302 may be configured to determine theavailability of solar energy in the vicinity of the local controllers308 and may be configured to act on that information. This informationmay be passed to users of the solar energy water heating systems 304 sothat, for example, if the information indicates that little or no solarenergy will be available the affected users can reduce their energyconsumption or modify their energy consumption to skew it towardsoff-peak hours. This information may be passed on automatically by thecentral control system 302 to the affected local controllers 308 forcommunication to associated users. For example, the information may bedisplayed on a display associated with each local controller 308.Alternatively this information may be passed on manually, eg. by email,by a person who receives it from the central control system 302 to usersof the affected solar energy water heating systems 304.

Another function that could be carried out by the central control system302 is to inform the utility company in situations where there is likelyto be an increased demand for electric power due to low availability ofsolar energy. The central control system 302 may be configured to sendcontrol signals to the local controllers 308 to adjust the usage of thenon-solar heating systems 104 according to the availability of solarenergy.

The central control system 302 may be configured to receive informationfrom the local controllers 308 regarding the amount of energy saved as aresult of solar energy water heating activity and/or the amount ofenergy consumed by use of the non-solar heating element and may beconfigured to cooperate with a billing system to reward and/or penalizeindividual users based on their activity. Optionally the feature ofrewarding and/or penalizing users may take into account the availabilityof solar energy during the time period being considered. Optionally, thecentral control system 302 can control the operation of the localcontrollers 308 based on the time of day, for example, to shift usage ofnon-solar heating elements to off-peak portions of the day. Instead ofcontrolling the local controllers 308 based on the time of day, thecentral control system 302 could additionally or alternatively monitorthe actual energy demand being place on the utility company in real timeand can adjust the usage of non-solar heating elements 104 as a way ofcontrolling the energy demand on the utility company.

Reference is made to FIG. 8, which illustrates a method 400 of heatingwater from a plurality of water storage tanks, in accordance withanother embodiment of the present invention. The method 400 may becarried out using the network 300 shown in FIG. 7, or may alternativelybe carried out by any other suitable means.

The method 400 includes a step 402 wherein a local controller isprovided in association with each water storage tank. The localcontrollers are each operatively connected to a non-solar heating systemfor the associated water storage tank and to a solar energy collectorsystem for the associated water storage tank. At step 404 a centralcontrol system is provided. At step 406, a selection is made of at leastone heating means from a group of heating means including the non-solarheating system and the solar energy collector. Step 408 includes heatingwater in each water storage tank using the selected heating means. Atstep 410, signals are sent at least one way between the central controlsystem and one or more local controllers, relating to the operation ofthe at least one local controller. These signals may be sent before,after or during the water in the water storage tanks is heated, or acombination thereof.

The signals may, for example, be instructions from the central controlsystem to the local controllers and may be based at least in part on theavailability of solar energy. The signals may, for example, beinstructions from the central control system to the local controllersand may be based at least in part on time of day.

The signals may, for example, may be from one or more local controllersto the central control system and may relate to one or more data relatedto the group consisting of: energy consumed by the non-solar heatingsystem, and energy saved resulting from use of the solar energycollector.

In any of the embodiments descried herein, in the event that excesssolar energy is available and is not needed for heating, structure maybe provided to divert the heat transfer fluid to another load, such asanother heat exchanger associated with a heating system for a swimmingpool, for example. The structure may include suitable valves which maybe controlled by the controller 24 or 102 or which may be controlled bysome other means, conduits to convey the heat transfer fluid to theother load and appropriate sensors.

In the embodiments described herein, the storage tank water exittemperature sensor has been described as being used to indicate thetemperature of water in the water storage tank. In at least someembodiments however, it may be possible to use a different temperaturesensor to obtain a suitable measurement. For example, when determiningthe amount of energy change that takes place in the water in the waterstorage tank, it may be possible to use the temperature history of theheat exchanger secondary inlet temperature sensor. It will be notedhowever, that this sensor may at certain times sense the temperature ofwater from the water source that is being sent to the water storage tankthrough the third storage tank port, which could affect the temperaturehistory.

While the above description constitutes a plurality of embodiments ofthe present invention, it will be appreciated that the present inventionis susceptible to further modification and change without departing fromthe fair meaning of the accompanying claims.

1. A solar energy water heating system, comprising: a water storagetank; a non-solar heating system configured to heat water in the waterstorage tank; a thermostat positioned to sense the temperatureindicative of the temperature of water in the water storage tank,wherein the thermostat is operatively connected to the non-solar heatingsystem; a solar energy collector; a heat exchanger; a first fluidcircuit between the solar energy collector and the heat exchanger; apump configured to pump fluid through the first fluid circuit; a secondfluid circuit between the water storage tank and the heat exchanger,wherein the heat exchanger is configured to transfer heat from fluid inthe first fluid circuit to water in the second fluid circuit, whereinthe second fluid circuit is fluidically connectable to a water source;and a controller configured to control the operation of the pump,wherein the controller is further configured to receive non-solarheating system state signals indicative of whether the non-solar heatingsystem is on and wherein the controller is configured to determine theamount of energy transferred from the solar energy collector to water inthe water storage tank based at least in part on the non-solar heatingsystem state signals.
 2. A solar energy water heating system as claimedin claim 1, wherein the controller is further configured to determinethe amount of energy transferred from the solar energy collector towater in the water storage tank based on the temperature of water in thewater storage tank, on the flow rate and temperature of any waterintroduced to the second fluid circuit from the water source, and on adetermination of the amount of energy introduced to the water in thestorage tank by the non-solar heating system.
 3. A solar energy waterheating system as claimed in claim 2, wherein the controller is furtherconfigured to determine the amount of energy introduced to the water inthe storage tank by the non-solar heating system based on the amount oftime the non-solar heating system is on and on the power of thenon-solar heating system.
 4. A solar energy water heating system asclaimed in claim 2, further comprising a storage tank water temperaturesensor, wherein the controller is further configured to receive from thestorage tank water temperature sensor signals indicative of thetemperature of water in the water storage tank, and wherein thecontroller is further configured to determine the amount of energytransferred from the solar energy collector to water in the waterstorage tank based in part on the temperature of water in the waterstorage tank.
 5. A solar energy water heating system as claimed in claim4, wherein the water storage tank has a consumption outlet and whereinthe storage tank water temperature sensor is positioned downstream fromthe consumption outlet.
 6. A solar energy water heating system asclaimed in claim 2, further comprising a source water temperaturesensor, wherein the controller is further configured to receive signalsfrom the source water temperature sensor indicative of the temperatureof water from the water source.
 7. A solar energy water heating systemas claimed in claim 2, further comprising a flow meter, wherein thecontroller is configured to receive flow meter signals from the flowmeter indicative of the flow rate of water into the second fluid circuitfrom the water source.
 8. A solar energy water heating system as claimedin claim 1, wherein the controller includes a display and is configuredto output on the display a value indicative of the amount of energysaved by heating water from the water storage tank with energy from thesolar energy collector.
 9. A solar energy water heating system,comprising: a water storage tank having a consumption outlet; anon-solar heating system configured to heat water in the water storagetank; a solar energy collector; a heat exchanger; a first fluid circuitbetween the solar energy collector and the heat exchanger; a pumpconfigured to pump fluid through the first fluid circuit; a second fluidcircuit between the water storage tank and the heat exchanger, whereinthe heat exchanger is configured to transfer heat from fluid in thefirst fluid circuit to water in the second fluid circuit, wherein thesecond fluid circuit is fluidically connectable to a water source; astorage tank water temperature sensor positioned downstream from theconsumption outlet; and a controller configured to receive signals fromthe storage tank water temperature sensor indicative of the temperatureof water leaving the water storage tank, wherein the controller isconfigured to prevent operation of the pump if the signals from thestorage tank water temperature sensor indicate the temperature of waterin the water storage tank exceeds a predetermined high storage tankwater temperature.
 10. A solar energy water heating system as claimed inclaim 9, wherein the predetermined high storage tank water temperatureis about 85 degrees Celsius.
 11. A solar energy water heating system,comprising: a water storage tank; a solar energy collector; a heatexchanger; a first fluid circuit between the solar energy collector andthe heat exchanger; a pump configured to pump fluid through the firstfluid circuit; a second fluid circuit between the water storage tank andthe heat exchanger, wherein the heat exchanger is configured to transferheat from fluid in the first fluid circuit to water in the second fluidcircuit, wherein the second fluid circuit is fluidically connectable toa water source; a solar energy collector temperature sensor positionedto sense temperature indicative of the temperature of the solar energycollector; a source water temperature sensor positioned to sensetemperature indicative of the temperature of water from the watersource; and a controller configured to receive solar energy collectortemperature sensor signals from the solar energy collector temperaturesensor and source water temperature sensor signals from the source watertemperature sensor, wherein the controller is configured to preventoperation of the pump if either the solar energy collector temperaturesensor signals indicate a solar energy collector temperature that isbelow a predetermined low solar energy collector temperature or if thesource water temperature sensor signals indicate a source watertemperature that is below a predetermined low source water temperature.12. A solar energy water heating system as claimed in claim 11, whereinthe predetermined low solar energy collector temperature is about 4degrees Celsius and wherein the predetermined low source watertemperature is about 4 degrees Celsius.
 13. A solar energy water heatingsystem as claimed in claim 12, wherein the first fluid circuit containsa fluid that is a mixture of propylene glycol and water.